The present invention generally relates to amorphous fluorinated carbon films and method of preparation and more particularly, relates to amorphous fluorinated carbon films that are thermally stable and have low dielectric constants suitable for use as insulating layers in electronic devices and a method of preparation of such films.
A semiconductor chip consists of an array of devices whose contacts are interconnected by patterns of metal wiring. For instance, in VLSI chips, the metal patterns are multilayered and are separated by layers of an insulating material which is characterized generally by a low dielectric constant Interlayer contacts between metal wiring patterns are made by through-holes which are etched through the layers of the insulating material. In a typical chip design, there are one or more wiring layers. Low dielectric constant insulating materials are employed between the wires in the same level and also between the various wiring levels.
In a typical VLSI chip, the insulating material is silicon dioxide that has a dielectric constant of between about 3.9 and about 4.1. As the speed of the chip is affected by the RC value of the insulator, enhanced speed performance requires reduction of the capacitance (C). The quest for higher integration in the chip results in the shrinkage of the dimension and tends to increase the capacitance values, unless the dielectric constant of the insulator is significantly reduced. Furthermore, with the increasing use of large scale integration in the chip design, back. end wiring densities are increasing. As the wiring density increases, the need for lower dielectric constant insulating materials, i.e. interlayer dielectric (ILD) materials arises in order to improve the performance of the VLSI and ULSI devices.
Different materials that have low dielectric constants have been investigated as potential replacement materials for silicon dioxide. For instance, among the candidate materials for the ILD, fluorinated carbon polymers appear to have the lowest dielectric constant values, i.e.,  less than 3. However, most of the materials with significantly lower dielectric constants such as those of fluoropolymers are thermally unstable at chip processing temperatures above 350xc2x0 C., thus making them unsuitable for integration in modem semiconductor fabrication technology. A thermal endurance at processing temperatures higher than 400xc2x0 C. after the deposition of the BEOL dielectric is frequently required in such technology.
It is therefore an object of the present invention to provide a low dielectric constant insulating material for use as a dielectric insulating layer in electronic devices that does not have. the drawbacks and shortcomings of the prior art dielectric materials.
It is another object of the present invention to provide a low dielectric constant material for use as a dielectric insulating layer in electronic devices that is thermally stable at semiconductor processing temperatures.
It is a further object of the present invention to provide a low dielectric constant insulating material for use as a dielectric insulating layer in semiconductor devices that is thermally stable in non-oxidizing environment at temperatures up to 400xc2x0 C.
It is another further object of the present invention to provide a low dielectric constant insulating material for use as a dielectric insulating material in both interlayer applications and intralayer applications in a semiconductor device that is thermally stable in non-oxidizing environment.
It is still another object of the present invention to provide a low dielectric constant insulating material for use as a dielectric insulating layer in semiconductor devices that has a dielectric constant of less than 3.0.
It is another further object of the present invention to provide a low dielectric constant insulator for spacing apart one or more levels of conductors in a semiconductor device.
It is still another further object of the present invention to provide a low dielectric constant amorphous fluorinated carbon material for use as a dielectric insulating layer in semiconductor devices that can be formed from a fluorinated cyclic hydrocarbon precursor.
It is yet another further object of the present invention to provide a low dielectric constant amorphous fluorinated carbon material for use as a dielectric insulating layer in semiconductor devices that can be formed from a fluorinated cyclic hydrocarbon precursor such as hexafluorobenzene, 1,2-thethynyltetrafluorobenzene or 1,4-bis(trifluoromethyl) benzene.
It is yet another further object of the present invention to provide a low dielectric constant amorphous fluorinated carbon material for use as a dielectric insulating layer in VLSI or ULSI devices that can be deposited by a radiation or beam assisted deposition technique.
In accordance with the present invention, an amorphous fluorinated carbon film for use as a dielectric insulating layer in semiconductor devices formed from a fluorinated cyclic is hydrocarbon precursor and a method of preparation are provided.
In the preferred embodiment, the amorphous fluorinated carbon film for use as a dielectric insulating layer is formed from a precursor selected from the group consisting of hexafluorobenzene, 1,2diethynyltetrafluorobenzene and 1,4-bis(trifluoromethyl) benzene. The film is prepared by a radiation or beam assisted deposition technique such as an ion beam assisted method, a laser assisted deposition method or a plasma assisted chemical vapor deposition method. The film deposited is thermally stable in non-oxidizing environment at temperatures up to 400xc2x0 C. and has a dielectric constant of less than 3.0. The film can be used as an interconnect dielectric layer in an electronic device, for instance, as an insulator for spacing apart conductors in an interconnect structure.
In an alternate embodiment, the amorphous fluorinated carbon film is deposited on an intermediate non-fluorinated diamond-like carbon layer or between two non-fluorinated diamond-like carbon layers.
In another alternate embodiment, an additional graded layer is deposited between the fluorinated carbon layer and the non-fluorinated diamond-like carbon layer
The present invention is also directed to an insulator used for spacing apart one or more levels of conductors in a semiconductor device which includes a substrate that has a top surface with an exposed first layer of metal, an insulator layer of amorphous fluorinated carbon formed from a fluorinated cyclic hydrocarbon precursor, and a second layer of metal that is patterned. to form a plurality of conductors on the insulator layer. The substrate may also have an upper surface with an exposed first area of metal and an exposed second area of an insulating material. The second area of insulating material is used for intra-level insulation purpose. The insulator may further include a graded layer between the fluorinated carbon layer and the non-fluorinated diamond-like carbon layer to improve the adhesion between the two dielectric layers. A continuous transition is provided by the graded layer between the two dielectric layers.
The present invention is further directed to an interconnect structure for use in a semiconductor device that includes a substrate, a first layer of an electrically conductive material deposited on the surface of the substrate, a layer of an amorphous fluorinated carbon deposited on top of the first layer of electrically conductive material from a fluorinated cyclic hydrocarbon precursor, a second layer of an electrically conductive material deposited on the amorphous fluorinated carbon layer, and a metal stud connecting the first layer of electrically conductive material to the second layer of electrically conductive material. The first and the second electrically conductive material can be aluminum, copper, tungsten, tantalum, titanium, their alloys and conductive metal nitrides. The layer of the amorphous fluorinated carbon has a low dielectric constant of smaller than 3.0 and some layers have a dielectric constant smaller than 2.8. It is thermally stable in a non-oxidizing environment at temperatures up to 400xc2x0 C. In one alternate embodiment, the layer of the fluorinated carbon is deposited on an intermediate non-fluorinated diamond-like carbon layer or between two non-fluorinated diamond-like carbon lathers. In another alternate embodiment, the interconnect structure also include a graded layer between the fluorinated carbon layer and the non-fluorinated diamond-like carbon layer.